Voltage gain control device



- June R L MacAUL-EY VOLTAGE GAIN CONTROL DEVICE Filed June 17, 1944 MINVENTOR.

Patented June 22, 1948 VOLTAGE GAIN CONTROL DEVICE Robert IrwinMacAuley, Passaic, N. J., assignmto Allen B. Du Mont Laboratories, Inc.,Passaio, N. 3., a corporation of Delaware Application June 17, 1944,Serial No. 540,873

4 Claims. (01. 250-27) 1 This invention relates to a device forcontrolling voltages. With this invention either alternating or directcurrent voltages can be varied continuously over wide ranges.Alternating current voltages of a very wide range of frequencies, in-

cluding very low frequencies, can be varied with-.

out the use of large coupling condensers, and no residual direct currentappears across this control device.

In carrying out the invention, a plurality of sets of electrodes whichmay be in the same or separate envelopes are employed with resistors inthe cathode circuits of said sets with a resistor coupling betweenintermediate points of said resistors. at least one of these pointspreferably being variable. The controlled voltage is taken of! of thislast named resistor.

The invention may be understood -from the description in connection withthe accompanying drawing, in which:

Fig. 1 is a diagram of connections showing an illustrative embodiment ofthe invention; and

Fig. 2 is a similar diagram showing a modification.

In the drawing, reference character 1 indicates a dual triode of whichthe plates 2 and 3 are connected to a source B of positive potential.The input terminal 4 is connected to the grid 5 of the first triode. Thecathode 6 of this triode is connected to ground through resistors l and8 which are connected in series.

A point ill of constant potential is connected to the grid l l of theother triode in the envelope 1, the cathode l2 of this triode beingconnected by series resistors l3, M and I5 to ground.

A point I6 is connected through resistor I! by means of a slidingcontact is to the resistor ll. The point [6 may be any point on resistorI. A sliding contact I! on the resistor I1 is connected to the outputterminal 20.

In the modification shown in Fig. 2. the parts that are common to Fig. 1are shown by the same reference characters with primes.

In this modification a resistor 22 is connected between a positivesource B and the plate 2', and this plate 2' is coupled by lead 23 toone end of two resistors 24 and 25 in series, the other end of theseresistors being connected to ground. A point between the resistors 2|and 25 is connected by lead 26 to the grid ll of the second triode inthe envelope l'.

The operation is as follows: The signal of which the amplitude is to bevaried is applied to the terminal 4 which is connected to the grid 5 ofthe dual triode l. The plates 2 and 3 are maintained at the samepotential while the potential applied at ID to the grid II is keptconstant. The gain control resistor I1 is connected between the point Itand a point on the resistor ll that is determined by the contact I8 sothat the desired voltage can be taken off of the resistor i1 byadjusting the contact 19. When a signal at terminal l is applied to thegrid 5, one end of the gain resistor control I! increases or decreasesin potential in accordance with the variation of the signal at thisinput terminal. The other end of this gain control resistor II will tendto remain at a fixed potential which depends upon the position of thecontactor l8 because the effective impedance of the cathode resistorsl3, I4 and I5 is small.

However, asmall signal is caused to appear at the contactor l8 due tothe voltage divider action of the gain control and part of the cathodeload in the second section of the resistors in the circult of thecathode l2. By utilizing the circuit shown in Fig. 2, this small signalis canceled. This is done by feeding a signal of proper phase andmagnitude to the grid H' of the second triode section instead of keepingthis grid at a constant potential as indicated in Fig. 1.

As illustrated in Fig. 2, a small plate load 22 in the first section ofthe dual triode l' provides a signal at its plate 2' that is of thecorrect polarity to change the potential applied by the lead 23,resistor 24 and lead 26 to the grid ll' so that the proper potential isapplied to the grid II' to cancel the distorting signal that mightotherwise appear at the contactor l8 of the gain control ll, l9.

What is claimed is:

1. A voltage gain control device which comprises two vacuum tubes atleast one of which has its anode connected directly to a source ofconstant potential, each of said vacuum tubes having an anode, a controlgrid and a cathode, one of said tubes having its. control grid connectedto a, source of constant potential and the other one having its controlgrid connected to a source of signal that is to be controlled, aresistance connected between each cathode and ground and a resistanceoff of which the output of said device is taken, said resistance beingconnected from a point on one of said cathode resistances between itsends and a point on the other cathode resistance between the endsthereof.

2. The device of claim 1 in which the anode of one of said tubes isconnected to said source of constant potential through a resistor.

4 3. The device 01 claim 1 in which a slidable .v (ms contact isprovided for said resistance oil. of which the output 01 said device istaken. The following references are of record in the v 4. The device 01'claim 1 m which a slidable file of this tent: contact is provided forsaid resistance of! of which UNITED the output of said device is takenand a. slidable a STATES PATENTS contact is providedsbetween one end ofsaid last Number Name Date named resistance and the resistance betweenthe 2364-197 Hamem 1941 cathode of one of said tubes and ground. 237L87538618? e 3, 1942 r 10 2,316,044 Blair Apr. 6, 1943 ROBERT mwm MAcAULEY.1 Kinsbura July 1a, 1943

